MISRA C:2012 Addendum 3 defines the coverage classification "Out of Scope" as "Aspects of behaviour are out of scope for C99 and are related to C11." Considering this definition, why is EXP46-C classified "Out of Scope"? It seems, there is no dependency of the rule to C11 at all.

I would actually argue that EXP46-C is covered by MISRA C:2012 essential type model explicitly and strong.

Are you planning an updated version of Addendum 3?
Is there a documentation of how MISRA came to their conclusions regarding the coverage decisions in Addendum3? I assume there is, so my question is more whether this is available publicly / on request?